Okay, a few clarifications.
If a player can spawn with a "sniper" rifle, buff his own damage to the max, climb to a nice spot high up, and snipe enemies, it's not necessarily bad, but it detracts from the team mentality. However, if a player can spawn with a "sniper" rifle, receive buffs from his team, climb to his vantage point and give covering fire, it's good teamwork.
That's a popular, but limited view of team mentality. A lot of people are suggesting that "teamwork" requires people to physically interact in some way. I can do all of your second example without recieving a buff from my team, and maintain that distance from my team without ever going back to get ammo, health, or buffs. It's then up to the particular memeber of the team that gives out said buffs to track me down and buff me if he feels the need, and it's my choice to go without if he does not. The buffs are a "forced" team mechanic.
By the no-scope comment, I was using it as an example to describe the idea of trick shots in general.... If they start going off by themselves, not helping with the objectives or the mission, I'll ignore them, and encourage my team to do the same.
I did know what you were getting at, but the first thing of note is that most snipers don't recognize quickscopers and trickshooters as snipers, which is why I pointed back to the unscoped weapons. The second thing of note is that with the SMART system the game is inviting that type of player in (whether or not they'll be successful is a different issue entirely) and they may well be valuable in some way, shape, or form. You not buffing them or telling your team not to buff them because you have yet to find that value makes you a bad teammate.
Finally, by "pure" I relate to the above: killing, not helping with objectives. Objectives give you the most experience, killing gives you the least. So a camper, or a trick-shot player, is going to have a rough time with this game if they don't help out with the mission. Hopefully this system will weed out the fools who came to this game just so they can use SMART to get cool-looking trick shots and high K/D.
It all comes back to working as a team and completing objectives. If every player on your team is working towards these two goals only, then it'll be a fun match. And really, I'd much rather have no snipers on my team at all, and have everyone working together, than have one sniper/camper who isn't doing his part to complete the objectives.
See that's where I have trouble with "pure". What leads to the assumption that a pure sniper is only about the killing and not the objective, and what leads to the assumption that killing is not helping with the objective?
It's an 8 man team, limiting the number of players harassing your team is a huge help. The amount of XP I get for it is irrelevant, that's my decision. If the team isn't trying to do the objective then "killing" is a problem (a team issue), but if even one person is trying to do the objective (because only one person can be actively doing an objective at any given time) then killing becomes important. Certainly there are places where said kills will be more effective, but unless you're sitting there over the snipers shoulder while he's making the kills you don't really know how important they are.
The goal of Brink is to get everybody playing the part they're comfortable with for the good of the team, that means killers recognizing how to make their skills more valuable to the team than just racking up unspecific kills, as well as objective players recognizing the value that the killer brings to the team and helping him make the most of it for the team.